1. Field of the Invention
The present invention relates to an ink composition that can improve the preservation characteristics (gas fastness) of an image to be produced, and, in more detail, to an ink composition containing phthalocyanine group cyan dye that can effectively prevent image fading.
2. Description of the Prior Art
Ink compositions using phthalocyanine group cyan dye have commonly been used in the past as superior ink compositions for coloring cyan images. Moreover, recently a widespread practice is to form an image using this kind of ink composition to color an image together with one or two or more ink compositions for coloring other colors, and to display the multi-color image thus obtained (color image) in a room, etc.
However, in ink compositions using this phthalocyanine group cyan dye, the phthalocyanine group cyan dye has poor fastness to the oxidizing gases present in the atmosphere such as ozone, nitrous oxide and sulfuric oxide, with especially poor ozone fastness. Therefore, when forming a multi-color image together with ink compositions of other colors and displaying said image in a room, there has been the problem that the image formed from said cyan dye fades rapidly.
Various types of ink compositions have been invented in order to prevent this kind of phthalocyanine fading. For example, in WO Patent Publication No. 99/50363 a cyan ink composition comprising copper phthalocyanine group cyan dye, imidazole derivative, anti-oxidation agent, sugar, and any naphthalene-1-sulfonate containing a hydroxyl group or amino group in position 4 is disclosed as a means to improve lightfastness (Patent Literature 1). However, this ink composition was not evaluated for ozone gas fastness, and has a hydrochloric acid group or amino group in the molecule of the components used, and for this reason has the problem that nitrous oxides (NOx gases) can cause the phenomena of turning the image green or black.
[Patent Literature 1] WO Patent Publication No. 99/50363
Consequently, an object of the present invention is to provide an ink composition that can improve the preservation characteristics (gas fastness) of an image produced by an ink composition using phthalocyanine group cyan dye.